2APB, 2-aminoethoxydiphenyl borate, a membrane-penetrable modulator of Ins(1,4,5)P3-induced Ca2+ release.

Although the specificity of 2APB with respect to the intracellular signaling system was not fully established, it is the first candidate for a membrane-penetrable modulator of Ins(1,4,5)P3 receptor, and it should be a useful tool to investigate the physiological role of the Ins(2,3,3)P2 receptor in various cells.